// Load a .jpg or .png file by adding .txt extensions to the file
// and dragging it on the imageTextAsset

var imageTextAsset : TextAsset;
function Start () {
    var tex = new Texture2D (4, 4);
    tex.LoadImage(imageTextAsset.bytes);
    renderer.material.mainTexture = tex;
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public TextAsset imageTextAsset;
    void Start() {
        Texture2D tex = new Texture2D(4, 4);
        tex.LoadImage(imageTextAsset.bytes);
        renderer.material.mainTexture = tex;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public imageTextAsset as TextAsset

    def Start():
        tex as Texture2D = Texture2D(4, 4)
        tex.LoadImage(imageTextAsset.bytes)
        renderer.material.mainTexture = tex